(Fair warning: If you haven't read The Pickwick Papers by Charles Dickens, this chapter won't make a lot of sense. We'll do our best to explain the references, but you might also want to read some of Dickens' novel to get the idea.)
Spring comes and the girls each tend a corner of the family garden. Each sister plants things and takes care of her garden in a way that reflects her personality – Meg's is pretty and simple, Jo constantly experiments, Beth grows things for the birds, her pet cats, and other animals, and Amy makes hers beautiful and elegant. Symbolism!
On rainy days, the girls hold meetings of their "Pickwick Club," which they call "the P.C." (Historical Background Lesson: The Pickwick Papers was Charles Dickens' first novel, published in the early nineteenth century, and apparently a favorite of the March sisters. It's an episodic story about Samuel Pickwick and his friends, who form a Pickwick Club at which they report on their travels throughout England. In the nineteenth century, there were many imitation Pickwick Clubs started by fans of the novel, so Jo and her sisters aren't the only ones to do this.)
During the meetings of the P.C., each of the girls impersonates one of the characters in The Pickwick Papers. Meg is Samuel Pickwick, Jo is Augustus Snodgrass, Beth is Tracy Tupman, and Amy is Nathaniel Winkle.
The P.C. produces a newsletter that they call The Pickwick Portfolio, in which each of the girls contributes articles. This is appropriate, since The Pickwick Papers is also about, well, papers. The clue's in the name!
At their meetings, Meg, as Mr. Pickwick, reads the paper they've produced this time to her sisters.
The edition of The Pickwick Portfolio that Meg reads in this chapter contains the following articles:
A poem celebrating the anniversary of the club, written by Jo.
A romantic tale about mistaken identity and marriage in Venice, written by Meg.
A joke about the club.
A recipe for baked squash, written by Beth.
A letter explaining why she hasn't written anything for the newsletter, by Amy.
A report of an accident that Meg had while getting firewood in the attic.
A description of the family's missing cat, Snowball.
A poem lamenting the lost cat, written by Jo.
A variety of announcements about things that are going to happen soon, such as Hannah teaching the girls to cook and Beth displaying the new doll's clothes she has made.
A comment on the behavior of each of the girls.
Meg, in the character of Samuel Pickwick, finishes reading each of these items from the paper and the girls applaud.
Jo gets up and, in the character of Augustus Snodgrass, proposes that they admit a new member to the club – Laurie.
The girls vote on the proposal. Beth and Jo are in favor of letting Laurie join them. Meg and Amy are against it – Meg is worried Laurie will laugh at them, and Amy is still young enough that she doesn't want to play with a boy.
Beth and Jo convince the girls to let Laurie join the club. They vote again, and everyone is in favor this time.
Jo opens the closet door and reveals Laurie, who has been hiding there the whole time.
Jo's sisters are a little irritated by the deception, but they're won over by Laurie, who immediately enters into the spirit of the club by announcing that he will play Sam Weller. (This is appropriate because Sam Weller is introduced in Chapter 10 of The Pickwick Papers, just as Laurie joins the March girls' Pickwick Club in Chapter 10 of Little Women).
Laurie announces that, as a token of his gratitude for being allowed to join the club, he is going to give them a post-office box. The box looks like a large birdhouse, and he has put it in the middle of the hedge between the March and Laurence houses. This "post office," or "P.O." for short, will let them exchange letters – partly for the club newsletter, and partly just for fun. It has a lock and Laurie holds one key, while the girls hold the other.
Laurie is an enthusiastic and wonderful member of the club, and the P.O. is a big hit.